1. Field of the Invention
The present invention relates to a gain control apparatus and method in a receiver of a wireless communication system; and, more particularly, to a gain control apparatus and method in a receiver of a multiband Orthogonal Frequency Division Multiplexing (OFDM) system.
2. Description of Related Art
In a wireless communication system, it is important in view of the entire system capacity to properly control the transmission power of a signal to be transmitted. Accordingly, when transmitting a signal, the wireless communication system transmits the signal at a proper transmission power. The receiver of the wireless communication system, therefore, should maximize the gain of a signal which is transmitted at a proper transmission power to restore the signal. A gain control method is typically used to properly restore a signal.
Due to development of a wireless communication technology, the wireless communication system has evolved from a method for transmitting data through only one band into a method for transmitting signals through a plurality of bands. A representative system of the signal transmission method using the plurality of bands is a wireless communication system using an Orthogonal Frequency Division Multiplexing (OFDM) signal, and a system with the plurality of bands is called a multiband system. Controlling the gain of a received signal is more important in the receiver of a wireless communication system using an OFDM scheme and the multiband more than a system using a single band.
The following description will be made with reference to the accompanying drawing on a method for controlling the gain of a reception signal in the receiver of the wireless communication system using the multiband.
FIG. 1 is a block diagram illustrating a typical auto gain control apparatus in a receiver of a wireless communication system using a multiband scheme.
A received signal is inputted to an auto gain amplifier 101. The auto gain amplifier 101 controls the gain of the received signal by a gain value according to the control of the auto gain controller 103 to output a gain controlled signal. The reception signal which is outputted through the above-described gain control operation is inputted to an analog-to-digital converter (ADC) 102. The ADC 102 converts an inputted analog signal into a digital signal and outputs the digital signal. The signal outputted from the ADC 102 is inputted to the auto gain controller (AGC) 103 and two different mixers 104 and 105.
First, the auto gain controller 103 compares the power level of the inputted digital signal with a predetermined reference value, controls a gain according to the difference between the power level and the predetermined reference value, and outputs the gain control result to the auto gain amplifier 101. This is how the auto gain controller 103 controls the gain. The mixers 104 and 105 are constituent elements for extracting a signal based on each band. The mixers 104 and 105 also determine the gain of a received signal based on a control power received from the band gain control circuit 106 and output the gain-determined signal. The band gain control circuit 106 receives a power level for each band from the modem controller 107, compares the power level with signal levels outputted from the mixers 104 and 105, and determines the gain values of the mixers 104 and 105 according to the comparison result. As described above, a gain control method based on bands in a receiver compares the received power level with a predetermined reference value for each band and performs auto gain control according to the comparison result, compensating the gain of the reception signal.
The above-described method should perform gain control for each band, calculate the average value of a power level for longer than a predetermined time, and compare the average value with the reference value. Consequently, an error may occur in a wireless communication system using a burst mode like the OFDM system where a state of each band rapidly changes according to time. Such an error may increase the number of retransmission times and decrease the total system throughput due to the increased retransmission. Accordingly, it is required to develop an apparatus and method capable of reducing an error when performing auto gain control for each band in a system in which a state of each band rapidly changes according to time.